At 750.5, the inner saucer of the Discovery matches the Constitution almost exactly, and the bridge modules are the same size.

An artist I follow came to around a 750 conclusion before the official numbers came out based on observations from the show. If you look at the shuttle bay and the size of the view screen when people are standing near it, it works out.

Tuskin38, I thought about that earlier but there is an issue with doing that in SE

With the astronaut test Harb and I do for scaling, it makes the Discovery 850m long

What I am thinking about doing is getting it to be 750m long from edge of the sauce to end of the nacelles and listing it as U.S.S. Discovery(750m) and having one that is more appropriately scaled at around 420m.

But I can't do one where the inner saucer matches the Connie saucer without making it nearly 1km long.

In other news I found a model I can't include, the SM file is 750MB and the model is heavily unoptimized but it certainly looks pretty.